The present invention relates generally to methods for joining structural and functional ceramic bodies to one another, and more specifically to a system and method for joining silicon carbide to itself using melting point assisted multiphase brazing so that the joined silicon carbide may be used, for example, as fuel cladding in nuclear reactors.
Ceramic materials are useful for certain demanding engineering applications due to their: (i) excellent strength at high temperature; (ii) resistance to chemical attack; (iii) inertness in radiation environments; and (iv) certain functional characteristics including optical properties, semiconductor properties and piezoelectricity. However, ceramics are not easily fabricated into complex shapes and, as a consequence, require advanced joining processes to integrate such materials into useful products. Joining silicon carbide to itself or other materials (e.g., other engineering ceramics, metals) is important for applications including manufacturing personal and vehicle armor, gas turbine engines, air breathing rocket engines, fusion reactors, and high temperature electronics. For use in the nuclear industry, various approaches have been investigated for joining silicon carbide to itself. However, these approaches have not been successful in addressing radiation damage and retaining joint integrity after irradiation.
Using silicon carbide (SiC) ceramic-matrix composites as the fuel cladding in light water reactors could lead to a very significant increase in the safety of existing reactors and transitioning from zirconium alloy nuclear fuel cladding to a silicon carbide composite cladding represents a significant shift in light water reactor materials technology. SiC is an important structural ceramic material owing to its excellent thermal and environmental stability, resistance to radiation, resistance to thermal shock, and high strength and toughness. Additionally, SiC is stable at temperatures in excess of 2,000° C. and does not melt under loss of coolant accident (LOCA) conditions. Furthermore, SiC does not suffer from fretting wear and produces very small amounts of hydrogen during oxidation in high temperature steam relative to presently used Zirconium alloys.
In addition to potentially improving safety, SiC has a lower neutron penalty than Zircaloy and may provide economic benefits if the same thickness of material is used in newly designed cladding. This may also allow for higher fuel burnups, thereby reducing the amount of nuclear fuel used by a reactor. Accordingly, SiC fuel cladding is considered to be an important strategic technology for advanced nuclear fuels programs. However, joining end plugs to cladding tubes for sealing in fuel pellets once they have been loaded into the fuel rods represents a remaining technical hurdle. This is an inherently difficult problem and acceptable technical solutions must be based on in-reactor conditions. Desired joint characteristics include mechanical robustness in commercial nuclear reactor conditions of 2250 PSI, at 350° C., in a water/steam environment, at neutron flux rate of about 1×1014 n/cm2-s (thermal+fast), for more than 6 years of service, and closure of the rod should be maintainable at temperatures of up to 1200° C.
Known technical approaches for joining SiC for use in nuclear environments include glass-ceramic bonding, displacement reaction bonding using Ti3SiC2, diffusion bonding with metallic foil inserts, and brazing using silicon containing materials. None of these approaches results in a product that can survive irradiation and flowing water tests that mimic in-service reactor conditions. Furthermore, these approaches require high pressures or extensive heating times to form mechanically sound joints, thereby making manufacturing difficult. Therefore, there is an ongoing need for a system and/or method that effectively joins silicon carbide to itself or to other materials to create assemblies for use in a variety of applications including fuel cladding in nuclear reactors.